Synthesis of side-chain monofluorinated amphetamines

Achieving regio- and stereo-control in the fluorination of aziridines under acidic conditions

We developed an efficient fluorination protocol that converts easily accessible aziridines into β-fluoroamines, which are important motifs in biologically active molecules. In contrast with traditional fluorination approaches, DMPU-HF has shown both higher reactivity and regioselectivity and good functional group tolerance; thus, a wide scope of β-fluoroamines can now be accessed conveniently. The stereochemical behavior of the ring opening depends on the substitution pattern of the aziridine substrate.

Nucleophilic Fluorination and Radiofluorination via Aziridinium Intermediates: N-Substituent Influence, Unexpected Regioselectivity, and Differences between Fluorine-19 and Fluorine-18

The efficient dehydrofluorination and radiofluorination of N,N-disubstituted-β-aminoalcohols through an anchimeric-assisted mechanism was developed. An investigation into the influence of N-substituents on the ring opening of the aziridinium intermediate indicated differences in the isomeric ratio and the yields of fluorinated products obtained from N,N-disubstituted-phenylalaninol. This influence was substantial for (18)F-radiofluorination, with yields varying from 0 to 71% at room temperature (RT). Although no significant effects were observed in the fluorine-19 chemistry when the reaction was heated to 90 °C, considerable changes appeared during radiofluorination. In the latter case, the radiochemical yields increased, and degradation of the 2-fluoro-propan-1-amine isomer (b) occurred, leading to a regiospecific reaction in the radiolabeling of [(18)F]-fluorodeprenyl. This method involving nucleophilic radiofluorination at RT was successfully applied to the radiolabeling of [(18)F]-2-fluoroethylamines in which the influence of the N-substituent was also observed.

Synthesis and biochemical evaluation of 3-fluoromethyl-1,2,3, 4-tetrahydroisoquinolines as selective inhibitors of phenylethanolamine N-methyltransferase versus the alpha(2)-adrenoceptor

A series of 3-fluoromethyl-1,2,3,4-tetrahydroisoquinolines (3-fluoromethyl-THIQs) was proposed, and their phenylethanolamine N-methyltransferase (PNMT) and alpha(2)-adrenoceptor affinities were predicted through the use of comparative molecular field analysis (CoMFA) models. These compounds were synthesized and evaluated for affinity at PNMT and the alpha(2)-adrenoceptor. It was discovered that these compounds are some of the most selective inhibitors of PNMT versus the alpha(2)-adrenoceptor known. To determine the ability of these compounds to penetrate the blood-brain barrier (BBB), a series of THIQs possessing a variety of calculated partition coefficients (Clog P) were assayed using an in vitro BBB model. This study found a good correlation between lipophilicity (Clog P) and BBB permeability, which indicated that THIQs possessing Clog P values of at least 0.13-0.57 should have some penetration into the brain. Two compounds [3-fluoromethyl-7-N-(4-chlorophenyl)aminosulfonyl-THIQ (18) and 3-fluoromethyl-7-cyano-THIQ (20)] possess calculated partition coefficients greater than 0.57 and display selectivities (alpha(2)-adrenoceptor K(i)/PNMT K(i)) greater than 200 and thus represent promising leads in the development of highly selective inhibitors of PNMT with the ability to penetrate the BBB.

Tissue levels and some in vivo responses to a monofluorinated analogue of amphetamine in the mouse

The metabolism and some behavioral properties of each of the optical isomers of 2-amino-1-fluoro-3-phenylpropane hydrochloride (fluoroamphetamine, FAM) were examined and compared to those of the optical isomers of amphetamine (AM). Substitution of fluorine into the side-chain of AM increased the rate of elimination of drug from brain and modified the kinetics from a one- to a two-compartment model. Urinary excretion of unchanged S-(-)-FAM was reduced from that observed after R-(-)-AM, suggesting a more extensive metabolism. Fluorine substitution also modified the behavioral response to AM. Thus, each optical isomer of FAM produced paradoxical reductions in locomotor activity and body temperature.

Comparison of the effects of amphetamine and a fluorinated analogue on locomotion and exploratory activity in the mouse

(+)-Amphetamine (AM) and its fluorinated analogue (+)-2-amino-3-fluoro-1-phenylpropane (fluoroamphetamine, FAM) were compared with regard to their effects on locomotor and exploratory activity in mice. Both drugs caused a reduction in spontaneous exploration, but this effect was more marked with FAM than with AM at 1 h after injection. Both compounds increased locomotor activity 10 min after injection, but FAM had sedative effects after 1 h, while AM continued to be stimulatory.

Some in vivo responses to a side chain monofluorinated amphetamine in the rat

Mature male or female Sprague-Dawley rats were injected intraperitoneally with various doses (0.005, 0.027 and 0.05 mM/Kg) of (+) amphetamine sulfate or (+)-alpha-fluoromethyl-beta-phenylethylamine hydrochloride. Core (rectal) body temperatures were measured at pretreatment and 30, 60, 90, 120, 180, 240 and 300 minutes after treatment. Injection of (+)amphetamine resulted in increased body temperatures in all dose groups excepting males in the low dose (0.005 mM/kg) group after which temperatures returned to and remained at control levels. Injection of (+)alpha-fluoromethylphenylethylamine resulted in initially increased temperatures in all dose groups and at 180 minutes reduced temperatures in high dose males and in medium and high dose females. Hypothermia was not observed after treatment with (+)amphetamine. These results suggest that (+)alpha-fluoromethyl-beta-phenylethylamine has chemical properties distinct from those of (+)-amphetamine.

Analysis of a monofluorinated analogue of amphetamine in brain tissue using gas chromatography with electron-capture detection

1. Difficulties encountered in the analysis of the monofluorinated amphetamine, 2-amino-3-fluoro-1-phenylpropane (AFP), are discussed. 2. A novel assay procedure and its application to the analysis of AFP in the rat brain are described. The procedure involves pentafluorobenzoylation of AFP under aqueous conditions and quantitation by a gas chromatography equipped with a capillary column and an electron-capture detector.